The present invention relates to power conservation in electronic devices, and more particularly in those making use of flash memory.
Daily use of electronic devices such as cell phones, laptops, personal digital assistants (PDAs), and digital music players is becoming increasingly widespread. A limitation on the ability to make full use of these portable devices is the battery life of the host device. As the electronics footprints becomes ever smaller, current leakage problems especially in extreme conditions are growing larger. Thus, electronic device and memory device design changes that can result in less current usage can have a beneficial effect on extending the useable life of the battery between charges.
One approach employed by computers is a hibernation/waken function that allows a computer to power down and subsequently restore processor state in executable memory after the computer power down without rebooting the operating system. Such a system is disclosed in U.S. Pat. No. 6,209,088 (Reneris).
With regard to removable data storage devices that do not require a boot up because operating system code is not stored on the device, the host can turn off the power supply to the data storage device to conserve on power. In the case of a flash device, such a complete termination of power to the device will cause a penalty in terms of latency. Delay is incurred upon turning the flash device back on because of the need to do a full mount.
In the case of a flash device that can decide by itself to enter a standby mode, the memory system RAM will need to remain awake so as to answer incoming host requests within the time constraints required by the host protocol. While power to most internal device processes may be stopped, if the RAM remains awake, the desired power conservation is compromised. Maintaining the current state in the RAM requires significant current thereby mitigating possible gains of the standby mode.